Power regulation in high-frequency heating apparatus



EXAMINER Z Sheets-Sheet 1 Thyrotron Rectifier Oscillator Vacuum Tube B.BOYD All ll. All VI I 1' XR Mum; (0S8 REFERENCE POWER REGULATION INHIGH-FREQUENCY HEATING AE'PARATUS Filed'Dec. 22, 1948 FIP8212 Aug. 4,1953 Fig. 3.

INVENTOR Bruce 80 d. BY y M MM- WITNESSES:

ATTORNEY POWER REGULATION IN HIGH-FREQUENCY HEATING APPARATUS Filed D90.22, 1948 B. BOYD Aug. 4, 1953 2 Sheets-Sheet 2 VIII! 8. mo. 5 mm 5 5 5 R8 H mm m m9 mm mm o n m l 5 5 H 5 m n. 5 6. no? 5 B. a

INVENTOR Bruce Boyd. BY,

ATTORNEY ITNE 7w- 4 Patented Aug. 4, 1953 POWER REGULATION INHIGH-FREQUENCY HEATING APPARATUS Bruce Boyd, Baltimore, Md., assignor toWestinghouse Electric Corporation, East Pittsburgh, Pa., a corporationof Pennsylvania Application December 22, 1948, Serial No. 66,822

My invention relates to high frequency electrical apparatus andparticularly to such apparatus as used in induction and dielectricheating, and the control thereof.

One of the difficult problems encountered in high frequency heating isthat of controlling the temperature of the material being heated withinnarrow critical limits. Absence of accurate and quick responsive controlwill often result in a defective article that must be scrapped. Not onlyis the raw material wasted, but also all the time and labor thatprecedes the heat treating step. In these days of high costs and neededproduction, such losses are even more acutely felt. For example, in theindustrial application involving the continuous operation of soldering acable sheath, the temperature of the work at the soldering point must bekept constant within critical limits. Since solder cools very rapidly, avariation in work speed or in heat generator output will very likelyresult in an open spot on the work. In the case of a cable sheath, ifthe flaw is not detected, 'the cablemight be installed underground andwill then certainly cause trouble. In order to detect and repair suchdefective spots at the point of manufacture, a lot of time and moneymust be spent.

It is also desirable, especially in.a continuous heat treatment process,to change the conveyor speed in order to match the optimum heatgenerator output to the size of material being heated. Thus for a givensize heat generator it is desirable to convey material at a faster ratethan 1" material of the same type, thereby gaining maximum possibleefficiency of the equipment. Regulation of the energy delivered to theheating point in response to changes in speed and size or type of workbeing heated is of .prime importance.

Attempts have been made to utilize a triode discharge device in the-gridcircuit of a high frequency oscillator to effect a change in oscillatorgrid bias in response to change in work load current. While such asystem is cheap enough for low power installations, it is renderedimpractical because of difficulties encountered in its stabilization.

It is accordingly the general object of my invention to provide aregulating system for a high frequency heat generator which is moreefficient and less expensive than those exemplified by prior art.

More specifically, it isan object of my inven-' tion to provide aregulator for a high frequency heat generator which will respond quicklyto effeet an appropriate change in the quantity of 6 Claims.

energy supplied to the work being heated at the heating point.

Another object of my invention is to provide a regulator system for ahigh frequency heat generator which will maintain the temperature of thework at the heating point substantially constant.

A further object of my invention is to provide a regulator system for ahigh frequency heat generator which will cause an optimum amount ofenergy to be delivered to the work being heated for a given work speed,size and type.

A still further object of my invention is to provide a device foreilicient regulation of energy delivered by a high frequency heatgenerator, responsive to energy being radiated from the work beingtreated.

Briefly stated my invention comprises the .comparison of a quantitywhich is a function of the load current of a high frequency heatgenerator with a quantity which is a function of a condition of the workbeing heated, and utilizing the resultant to effect a rapid correctionin the output of the high frequency generator.

My invention, together with additional objects and advantages thereof,will best be understood from the following description when read inconnection with the accompanying drawings, in which:

Figure 1 is a block diagram of a preferred embodiment of my invention.

Figure 2 is a schematic circuit diagram of a preferred embodiment of myinvention.

Figure 3 is a schematic showing of a thermopile device, which may beused in one embodiment of my invention.

Figure 4 is a schematic showing of a photoelectric pick-up device whichmay be used in another embodiment of my invention.

The block diagram of Figure 1 illustrates an embodiment of my inventionin which it is desired to maintain a constant work temperatureregardless of the type or size of the work being treated or the speed atwhich it is being conveyed past the heating point. The system includes aconveyor l which conveys work to be heated into the control unit, one ofwhich is derived from the thyratron rectifier circuit and isproportional to the oscillator generator load and the other is derivedfrom a tachometer I1 whose shaft I9 is physically connected to theconveyor I and which is proportional to the conveyor speed. Theresultant of these voltages determines the direction and degree ofrotation of the motor I5, and hence the degree and sense of the phaseshift, and therefore the rectifier 1 and oscillator generator output.

Referring now to Figure 2, the high frequency oscillator generatorcircuit indicated generally at 5 includes a triode oscillator tube 2|,which may, for example, be type WL-892 having an anode 23, a cathode 25and a grid 21.

An inductance 29 and a capacitor 3| are connected in series between thegrid 21 of the oscillator tube 2! and ground 33. A grid bias resistor 35is connected from the cathode 25 to a point 31 common to the lastmentioned inductance 29 and capacitor 3|. There is a connection betweenthe junction 39 of the grid bias resistor 35 and the cathode 25 toground 4|. The oscillator generator tank circuit indicated generally at43 comprises an inductance 45, a capacitor 41, and a work coil 3connected in series. A coupling capacitor 24 is connected from a point49 between the tank circuit inductance 45 and capacitor 41 to the anode23 of the triode oscillator tube 2|. The capacitor 41 side of the workcoil 3 is connected to ground 42. The work being treated is passedthrough the work coil 3 on a conveyor indicated generally at I.

Power is supplied to the oscillator generator by a thyratron rectifierindicatedgenerally at 5| which includes six thyratron tubes 53, 55, 51,59, BI, and 63, each having an anode 65, a cathode 61, and a grid 69.

These six thyratron tubes are connected in three parallel groups 13, I5,11 of two tubes each of which are connected in series. The grid of onlyone tube in each group is controlled. The output of the thyratronrectifier 5| is fed to the oscillator generator 5 through a couplinginductance 19 which has one side connected to the oscillator tube anode23 and the other side connected to the cathodes 61 of the gridcontrolled thyratrons 53, 55 and 51. A bypass capacitor H is connectedfrom the thyratron cathode side of the coupling inductance 19 to ground18.

Three phase A. C. power is supplied to the thyratron rectifier throughthree coupling transformers 92, 94, 96, whose primaries I90 are deltaconnected and whose secondaries 98 are star connected. A leg 85, 81, 89of the star being connected to a point between the anode 65 of acontrolled thyratron 53, 55, 51 and the cathode 61 of the correspondingnon-controlled thyratron 59, GI, 63 of each series thyratron group 13,15, 11 respectively. The vertices of the delta are connected one to eachprimary leg II3 of the phase shifter III.

The three phase control voltage is supplied to the grids 69 of thecontrol thyratrons 53, 55, 51 through three grid coupling transformers9|, 93, 95. The secondaries 91 of these transformers are star connected,each leg 99, IIJI, I63 of the star being connected to the grid of acontrolled thyratron tube 53, 55, 51 respectively. The primaries I05 ofthe grid coupling transformers are delta connected, the vertices I01 ofthe delta being connected to the secondary legs I09 of a phase shifterindicated generally at I I I.

The primary legs II3 of the phase shifter III 4 are connected through aswitch II4 to 3 phase power source H5.

A negative grid bias is supplied to the controlled thyratrons from anyconvenient source 8| which is connected from the cathode 61' of thecontrolled thyratrons 51, 53, 5| to the neutral or the grid couplingtransformer secondaries.

The shaft of the phase shifter I I I is physically connected to therotor shaft II of a reversible motor I5 which drives the phase shifter.

The reversible motor I5 may be of the shaded pole single phase A. C,induction type. single phase A. C. power is supplied to the fieldwinding of the reversible motor by appropriate connections II1, througha switch I20, to a convenient source II9.

A pair of double pole double throw switches I45, I41 are provided sothat the reversible motor I5 may be either manually controlled by meansof push button switches, or automatically controlled by the control unitI3 heretofore mentioned. One side of the center poles of these switcheshave a common appropriate connection I21 to the reversible motor I5. Theother side of the center poles each have a separate appropriateconnection I 24, I26, to the reversible motor I5. There is a push buttonswitch H6, H8 connected across one pair of the end poles of each switchI45, I41.

When the double pole double throw switches I45, I41 are closed to themanual operating position, the motor may be manually controlled byclosing the appropriate push button switch I I6 or II8. When the doublepole double throw switches I45, I41 are closed to the automaticoperating position, the direction of rotation of the reversible motor iscontrolled by a pair of relays I2 I, I23. The other end poles of thedouble pole double throw switches I45, I41 are connected, each pairacross the stationary contacts of one of these relays I2I, I23. Themovable contacts of the motor relays I2I, I 23 are each actuated by asolenoid coil I3I, I32 which is located in the plate circuit of thecontrol unit as will be more fully explained hereinafter.

The control unit for controlling the direction and degree of rotation ofthe reversible motor I5, indicated generally at I3, includes a pair ofthyratron tubes I33, I35 which may be of the type 2050 each having ananode I31, a cathode I39, a control grid MI, and a suppressor grid I43.The suppressor grids I43 are connected together and are common to thecathodes I39 which are also connected together. Connected in seriesbetween the anode I31 of the first control unit thyratron tube I33 andthe anode I31 of the second control unit thyratron tube I35 is a relaysolenoid coil I32, a resistor I53, another resistor I55 and a relaysolenoid coil I3I respectively. These relay solenoid coils E32, I3I areby-passed by capacitors I49, I5I. The purpose of the resistors I53, I55is to limit the relay solenoid coil I3I, I32 current. The purpose of thecapacitors I49, I5I is to produce an inertia effect on the relaysolenoid coil current when the reversible motor I5 is being operated bythe control unit, which will be more fully explained hereinafter. Anodevoltage is supplied to the control unit thyratron tubes I33, I35 througha transformer I51 whose secondary I59 is connected between a pointcommon to the cathodes I39 of these tubes and a point common to thesolenoid coil current limiting resistors I53, I55, and whose primary IGIis connected through a switch I29 to a single phase A. C. source H9, Thegrids I 4| of these rent.

tubes I33, I35 are connected to the capacitorresistor junctions of acircuit which includes two capacitors I63, I65 connected together inseries with four resistors I61, I69, I1I, I13. There is a connectionbetween a point common to these capacitor I 63, I65 and a point commonto the control unit thyratron tube cathodes I39. The purpose of thecapacitors I63, IE5 is to stabilize the thyratron tubes. The purpose ofthe two resistors I61, I13, which are connected nearest to thecapacitors, is to limit the thyratron grid our- The purpose of the othertwo resistors I69, I1I is to limit the contact current of a polarizedrelay indicated generally at I35 whose stationary contacts I11, I19 areconnected to the noncommon ends of these resistors I99, Ill. The movablecontact I8I of the polarized relay I15 is connected through thesecondary I83 of transformer I85 to a point common to the relay contactcurrent limiting resistors I59 and I'iI. The primary I81 of thistransformer is connected through a switch I 29 to a single phase A. C.supply line II9.

One coil I39 of the polarized relay is connected to an A. C. tachometerI1 whose shaft I9 is physically connected to the conveyor I. A rectoxelement I93 and a filter circuit are connected between this relay coilI89 and the tachometer I1 for the purpose of rectifyingand smoothing outthe voltage generated by the tachometer.

The filter circuit comprises two capacitors 95, I91, and a potentiometerI39. One of these capacitors I95 is connected acros the relay coil I89.The potentiometer I99 is connected from one side of this capacitor I95through the rectox unit I 93 to the tachometer I1. The other capacitorI91 is connected so as to have one side common to the other side of thefirst mentioned capacitor I95 and the other side common to thepotentiometer and the rectox unit I93.

In series with one side of the other polarized relay coil IQI are apotentiometer HI and a resistor 203.

The purpose of the resistor 203 is to provide a potential drop which isproportional to the oscillator generator load current. The side of thisresistor 203 common to the potentiometer 2DI is connected to ground asshown at 255, and the other side is connected to the anodes 65 of thenon-controlled thyratron rectifier tubes 59, 5E, 63. The other side ofthis polarized relay coil I9I is connected to the movable element 291 ofa voltage divider 289. One side of this voltage divider 209 i connectedto the anodes 65 of the non-controlled thyratron rectifier tubes 59. GI,63, and to the cathodes 39 of the thyratron con trol tubes I 33, I35,while the other side is connected to a point common to the polarizedrelay contact current limiting resistors I69, Ill.

The purpose of the voltage divider 289 is to apply a constant voltagebias to one coil of the polarized relay for reasons hereinafter to bemore fully explained, and a constant negative bias to the grids MI ofthe control unit thyratron tubes. I33, I35. The voltage which i suppliedto the voltage divider is derived from a full wave rectifier tube 2IIwhich may be type 5114 having a cathode 2 I3 and two anodes 2l5. Onesecondary winding 2I1 of a multi-secondary transformer, indicatedgenerally at 2I9, is connected between the two anodes 2I5 of thisrectifier tube 2| I. A center tap is taken from this secondary winding 2I 1 through a potentiometer 22I to the side of the voltage divider 209which is common to the relay coil current limiting resistors 59, I1I. Afilter circuit comprising a pair of capacitors 223, 225,

an iron core inductance 221, and the potentiometer 22I last mentioned isprovided in the output circuit of the full wave rectifier for thepurpose of furnishing a smooth D. C. bias to the polarized relay coilI9I. One of these capacitors 225 is connected across the voltage divider289. The iron core inductance 221 is connected between the full waverectifier cathode 2I3 and the control unit thyratron cathodes I39. Theother capacitor is connected between the thyratron cathodes I39 and thetransformer center tap side of the potentiometer 22I. A winding 229 ofthe multi-secondary transformer 2I9 is connected across the cathode 2I3of the full wave rectifier to supply cathode voltage thereto. A thirdsecondary winding 23I of the multi-secondary transformer 2 I 9 isprovided to furnish cathode voltage to the two control unit thyratrontubes I33, I35, which cathodes are connected in parallel across thatwinding. The primary 233 of the multisecondary transformer is suppliedthrough a switch I20 from a single phase A. C. source II9 Although manyapplications of my invention will be apparent to those skilled in theart, it will be assumed for the purpose of explaining its operation,that it is desired to solder a cable sheath in a continuous operation.Referring now to Figure 2, assume that both reversible motor relayswitches I2I, I23, are open, that the double pole double throw switchesI45, I41 are in position for automatic operation of the reversible motorI5, that the phase shifter III is in a position to cause maximum powerto be delivered from the thyratron rectifier 5|, and that the polarizedrelay I15 is in neutral position, and the conveyor I is stopped. Tobegin operation, the single phase A. C. power circuit II9 is closed bymeans of switch I29, whereupon the reversible motor I5 field winding isenergized, cathode voltage is supplied, through one secondary winding23I of the multi-secondary transformer 219 to the control unit thyratrontubes I33, I35, and through another secondary winding 229 of the sametransformer to the full wave rectifier tube 2I I. Anode voltage issupplied through the appropriate coupling transformer I51 to the controlunit thyratron tubes I33, I35, and the primary winding I81 of thecontrol unit grid coupling .transformer I85 is energized. Anode voltageis supplied through a secondary winding 2I1 of the multi-seoondarytransformer M9 to the full wave rectifier 2.

The three phase supply circuit II5 is closed by means of switch II4,thereby energizing the thyratron rectifier anode coupling transformers92, 94, 96 and the phase shifter III.

The full wave rectifier 2 now operates to put a D. C. voltage across thevoltage divider 299. The D. C. voltage of the voltage divider is appliedin the grid circuits of the control unit thyratrons to establish anegative cut-off bias on the grids of those tubes. An amount of this D.C. voltage sufficient to cause the polarized relay I15 to close to itsleft-hand contact I11 is tapped oil? the voltage divider 209 and appliedto the appropriate polarized relay coil I9I. The closing of thispolarized relay contact I11 causes the secondary voltage of the gridcoupling transformer I85 to be applied across the lower polarized relaycontact current limiting resistor I69. Now when on the first positivehalf cycle, the A. C. voltage exceeds the D. C. bias voltage, thecapacitors I63, I65 in the control unit grid circuits will be charged sothat there is a positive bias on the grid I4I of the lower amplifiertube I35 sufficient to cause it to fire, and a negative bias on the gridI 4| of the upper amplifier tube I33 sufiicient to prevent its firing.Then as the A. C. anode voltage of the firing amplifier tube I35 passesthrough zero, that tube will cease to fire.

So long as the polarized relay I15 contacts are closed to the left sideI11, the lower amplifier tube I35 will fire on every positive half cycleand the upper amplifier tube E33 will not fire at all.

The firing of the lower amplifier tube causes a series of voltage pulsesto be placed across the coil I3I of the lower reversible motor controlrelay I23. The capacitor II which is connected across this coil gives aninertia or smoothing effect which prevents chatter of the relay I23. Theclosing of the lower reversible motor relay I23 will cause thereversible motor I5 to rotate the phaseshifter III in the direction todecrease the firing time of the thyratron rectifier controlled tubes 53,55, 51 and thus reduce its power output, and hence the power output ofthe oscillator generator 5 and the heat generated in the cable sheathbeing soldered.

Now after a time delay suitable to allow the solder and cable sheath toreach the proper soldering temperature (by means not shown) the conveyorI is started. When the conveyor I has reached the proper running speedfor the size and type cable sheath being soldered, the tachometer I1which is responsive to conveyor speed, will be generating a voltagesufiicient to pull the polarized relay IBI back to neutral position.This voltage will be sufiicient to balance the potential tapped from thevoltage divider 209 plus the potential furnished by the oscillator anodecurrent across its voltage dropping resistor 203.

Next assume that the speed of the conveyor I has increased so that it isnecessary to deliver more energy to the cable sheath in order tomaintain proper soldering temperature. Then the tachometer voltage willincrease and pull the polarized relay I contact closed to the right sideI19, thus placing the control unit thyratron A. C. grid voltage acrossthe upper polarized relay contact current limiting resistor IN. Thiswill cause the upper amplifier tube I33 to fire in the manner previouslydescribed, thus closing the upper reversible motor relay I2I contacts tocause the motor I5 to rotate the phase shifter III in the direction toincrease the firing time of the controlled thyratron rectifier tubes 53,55, 51, increasing its output and therefore increasing the oscillatorgenerator 5 output and the energy supplied to the cable sheath beingsoldered. When the oscillator anode current has been increasedsufilciently to cause its dropping resistor 203 potential to increase soas to balance the voltage generated by the tachometer I1 at theincreased conveyor speed, then the polarized relay I15 will be pulledback to its neutral position, opening the control unit circuit andtherefore the reversible motor I5 circuit causing the phase shifter IIIto come to rest.

Now if the conveyor speed should decrease the voltage generated by thetachometer I1 will decrease and the polarized relay I15 will operate tocause a decrease in energy delivered to the cable sheath being soldereduntil the polarized relay I15 has again been returned to neutral by adecrease in oscillator anode current in the same manner as has beenpreviously explained.

'In applications of my invention where the work temperature isrelatively high so as to be within their sensitivity range, I find itdesirable to use a photoelectric pick-up device or a thermopile as thework condition responsive means.

The photo-electric pick-up device shown schematically in Fig. 4 includesa photo-electric tube 250, which may be type 918, and which is placed inproximity to the work being heated at the heating point, so that it isresponsive to the intensity of light being radiated from the work due toits temperature condition.

The energy derived from the photo-electric tube 250 is subjected to twostages of D. C. amplification. The first D. C. amplifier stage includesan amplifier tube 252 which may be of type 6AC7, having an anode 254, acathode 256, a control grid 258, a screen grid 260, a suppressor grid26I and a heater 262. The second D. C. amplifier stage includes anamplifier tube 264 which may be of type 6B4-G, having an anode 266, acathode 266, a control grid 210 and a heater 212. Anode voltage and gridbias is supplied to the amplifier tubes by a full wave rectifier whichincludes a full wave rectifier tube 214 which may be of type 5U4-G and afilter circuit indicated generally at 216 for smoothing out the fullwave rectifier tube output.

Power is supplied to the full wave rectifier and to the amplifier tubeheaters 262, 212 by a multisecondary transformer 218 having threesecondary windings whose primary 280 is connected through a switch 282to a convenient A. C. source 284. One of the secondary windings 286 ofthe multi-secondary tansformer is connected across the heaters 262, 212of the amplifier tubes 252, 264, while another secondary winding 288 isconnected across the cathode 290 of the full wave rectifier tube 214.The ends of the third secondary winding 292 are connected each t ananode 294 of the full wave rectifier tube 214.

The filter circuit of the full wave rectifier comprises two capacitors290, 298 and two iron core inductances 300, 302. One end of thecapacitors 295, 298 has a common connection to a center tap on therectifier tube anode supply secondary winding 292 of the multi-secondarytransformer 218. One of the iron core inductances 300 is connectedbetween the other ends of the capacitors 296, 298. One side of the lastmentioned iron core inductance 300 is connected through the other ironcore inductance 302 to the cathode 290 of the full wave rectifier tube214. There is a connection from the rectifier tube anode supplysecondary winding 292 center tap which is the low voltage side of therectifier output, through a two tap voltage divider 304 and then througha single tap voltage divider 306 to the side of an iron core inductance300 which is common to one end of a capacitor but not common to theother iron core inductance 302 which is the high voltage side of therectifier output. A voltage regulator tube 308 which may be type VR- isconnected across the two tap voltage divider 304 in a manner such thatits cathode 3I0 is common to the rectifier tube anode supply secondarywinding 292 center tap and its anode 3I2 is common to the two tapvoltage divider 394 and the single tap voltage divider 306. There is aconnection from the grid 258 of the first amplifier tube 252 through agrid bias resistor 3I4 to the voltage regulator cathode 3I 8 side of thetwo tap voltage divider 304. The photo-electric tube 250 has its anode3I6 connected to the control grid 253 and its cathode 3I8 connected tothe screen grid 2 60 of the first amplifier tube 252.

The cathode 256 of the first amplifier tube 252 is connected to the tap320 of the two tap voltage divider 304 which is nearest the low voltageside of the rectifier output. The screen grid 360 of the first amplifiertube 252 is connected to the other tap 322 of the two tap voltagedivider 304, and the'suppressor grid ZIiI is connected to the cathode 256. The first amplifier stage is coupled to the second amplifier stageby means of a cou: pling resistor 32: which has one side common to thefirst amplifier tube anode 254 and the second amplifier tube grid 210and the other side common to the voltage dividers 304, 306. One coil I89of a polarized relay I15 is connected between the anode 266 of thesecond amplifier tube 254 and the high voltage side 3215 of the singletap voltage divider 306.

For the purpose of describing the operation of the embodiment of myinvention in which a photo-electric pick-up device is used as the workcondition responsive means, assume that such a device as shown in Fig. 4has been connected to one coil I89 of the polarized relay I15 in lieu ofthe tachometer circuit shown in Figure 2 and the reversible motor I5connections I24, I21, I26 have been reversed so that when the uppermotor relay !32 is closed the motor I5 will rotate the phase shifter l Il in the sense to decrease the thyratron rectifier 5I output. Assumealso that both reversible motor relay switches Igl, I23 are open, thatthe. double pole double throw switches I45, I41 are in position forautomatic operation of reversible motor I5, the phase shifter III is ina position to cause maximum power to be delivered from the thyratronrectifier BI, the polarized relay I15 is in neutral position, theconveyor I is ed. an the p te-e e i d e h s b ep energized by theclosing of its A. C. power supply circuit by means of an appropriateswitch 232,

To begin operation, the remainder of the equipment is energized in themanner set forth in the description of the operation of the firstembodiment of my invention. When the work temperature reaches a valuesuch that the intensity of light radiated from the work is within thesensitivity range o t e ph te-e eeirie t .59 h

' the voltage developed across that tube endanplied between the control2 5g andscreen grids Q69 o th fir t am l fier e 5? wil upset the ties aance o t e l st ment oned tube 252 eaasiee i to e nd e h ou ut at thfirst amp ifies" sta e i am l f ed by t a fier stage and a p i d to th it head polarized rela o l T p t n of th va -bas vide 39. whic i een eiedin ser es w th the eft hea po r e r l y oi I91 i adjust d o that 5. v ae app to i rela soi -W t e polarized relay I15 to be balanced when thework is at the desired temperature. The yoltage drop from the oscillatoranode current QIQQPPil'lg resistor 203 is reduced to zero for this formof operation. This may be done in any convenient manner, for example, bymeans of a switch 204 connected in shunt with the resistor 203.

When the work temperature reaches the point for which the system hasbeen calibrated there will be sufficient current produced in the righthand polarized relay coil I89 to pull the relay contacts to neutralposition.

Should the work temperature exceed the calibrated temperature thephoto-electric pick-up device will produce an output sufficient to closethe polarized relay contacts to the right hand side I19 which willoperate the equipment in the manner heretofore described so as to reducethe output of the oscillator generator 5.

aesteee When it is desired to use a thermopile as the work conditionresponsive element, such a device as is shown in Fig. 3 may be employed.It will be noted that the circuit shown in Fig. 3 is identical to thatshown in Fig. 4 except that the photoelectric tube 250 has beeneliminated and the grid bias resistor SM is replaced by a thermoelement328 whose resistance is a function of its temperature. Thisthermo-element 328 is placed in proximity to the Work being heated atthe heating point, so that it is responsive to the intensity of heatbeing radiated from the work due to its temperature condition. When thethermopile circuit is energized and the work is cold, then theresistance of the thermal element 328 is such that the first amplifiertube 252 will be biased to cut-off. When the. work is heated, thethermo-element 328 will also be heated and its resistance will decreaseso as to cause the grid 258 of the first amplifier tube 252 to becomepositive with respect to its cathode 256 and the tube will conduct, withthe result that current will fiow in the polarized relay coil I89 of ainagnitude proportional to the work temperaure.

The connections and operation of the equipment utilizing the thermo-pileembodiment of my invention is otherwise identical to that of thephoto-electric device embodiment which has been heretofore described.

It will be clear from the foregoing description of illustrativeembodiments of my invention that I have devised a regulator system forhigh frequency generators which will respond rapidly to variations inthe system parameters to correct the high frequency generator output soas to maintain the work being treated at a substantially constanttemperature, irrespective of such variations.

it will be understood that the embodiments of my invention which I haveshown and described herein are merely illustrative of my invention, andit will be apparent to those skilled in the art that certainmodifications may be made without departing from the spirit and scope ofmy invention.

My invention may be used in dielectric as well as induction heatingapplications. The phase shifter may be replaced by an inductionregulator, or a saturable reactor.

My invention, therefore, is not to be restricted except insofar as isnecessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. In a system for high frequency dielectric heating of work to beconveyed at a variable rate between a pair of electrodes, thecombination comprisinga high frequency oscillation generator having apower output tube and an output circuit disposed to supply highfrequency potential to said electrodes, a power supply including anelectric discharge device having a control grid and connected ,tocontrol the power output tube of said high frequency generator, meansfor deriving a voltage proportional to the speed of said work, means forderiving a voltage proportional to the power supply electric dischargedevice load current, and means responsive to the resultant of said lastmentioned voltages and connected to said control grid for changing thepower supply output, whereby the work temperature will be maintained ata substantially constant value, irrespective of variations in the speedof said work.

2. In a system for high frequency induction heating of work to beconveyed at a variable rate through a work coil, the combinationcomprising a high frequency oscillatory generator having an outputcircuit disposed to supply high frequency potential to said work coil, apower supply including an electric discharge device having a controlgrid connected to said high frequency oscillatory generator, means forderiving a voltage proportional to the speed of said work, means forderiving a voltage proportional to the power supply electric dischargedevice load current, and means responsive to the resultant of said lastmentioned voltages and connected to said control grid for changing thepower supply output, whereby the work temperature will be maintained ata substantially constant value, irrespective of variations in the speedof said work.

3. In a system for controlling the heat supplied to work being conveyedpast a predetermined point, the combination comprising an oscillatorgenerator including at least one electric discharge device which ananode and a cathode and having an output circuit disposed to supplyenergy at said predetermined point, a means including a rectifier havinga control electrode and connected for supplying a control potentialbetween said oscillator anode and cathode, first connections forderiving a voltage proportional to the speed of said work, secondconnections including a voltage dropping device in the plate circuit ofsaid oscillator for obtaining a voltage proportional to said oscillatorplate current, a means for comparing said voltages, and a meansresponsive to the resultant of said voltages and connected to thecontrol electrode of said rectifier for controlling the output of saidoscillator generator.

4. In a system for controlling the heat to be supplied to work beingconveyed past a predetermined point, the combination comprising anoscillator generator including at least one electric discharge devicewhich has an anode, a cathode and a grid and having an output circuitdisposed to supply energy at said predetermined point, at least oneelectric discharge device having a control grid and connected forsupplying a control potential between said oscillator anode and cathode,means for deriving a voltage proportional to the speed of said work,means for deriving a voltage proportional to said potential between saidoscillator, anode and cathode, a means including a polarized relay forcomparing said last mentioned voltages, and means responsive to theresultant of said voltages and connected to the control grid of saidelectric discharge device for varying the output of said oscillatorgenerator.

5. In combination, a first electric discharge device having an anode andadapted to produce a variable output, a means including a phase shiftorconnected to said first electric discharge device for varying saidoutput, a reversible motor rotatably connected to said phase shifter, apolarized relay having two coils and two contact positions and connectedto control the direction of rotation of said motor, a high frequencygenerator connected to the output of said first electric dischargedevice and having a tank circuit including a work coil through whichwork to be heated is conveyed at a variable speed, means for placing avoltage proportional to the speed of said work on one coil of saidpolarized relay, and means including a second electric discharge devicefor deriving a voltage proportional to said first electric dischargedevice anode current for placing a voltage on the other coil of saidpolarized relay, whereby the temperature of the material being heatedwill be regulated to maintain a constant value at the heating point.

6. In a system for regulating the work temperature in the heat treatmentof work to be conveyed at a variable rate through a heater unit, thecombination comprising a source of high frequency oscillations includinga power output tube having an anode, an output circuit connected to saidpower output tube and disposed to deliver heat energy to said heaterunit, a gaseous discharge device having a control electrode and adaptedto control the output of said power output tube, means for deriving areference voltage which is proportional to the output of said poweroutput tube required to maintain the desired work temperature, means forderiving a second voltage which varies in response to variations in thevelocity of said work, means for comparing said reference voltage andsaid second voltage, and means responsive to the comparison resultant ofsaid voltages and connected to the control grid of said gaseousdischarge device for varying the output of said source of high frequencyoscillations.

BRUCE BOYD.

References Cited in the file Of this patent UNITED STATES PATENTS NumberName Date 2,041,029 Stargardter May 19, 1936 2,175,694 Jones Oct. 10,1939 2,205,424 Leonard June 25, 1940 2,251,277 Hart et a1. Aug. 5, 19412,325,401 Hurlston July 27, 1943 2,391,085 Crandell Dec. 18, 19452,419,214 Holman et a1. Apr. 22, 1947 2,436,027 Vonada et al Feb. 17,1948 2,448,008 Baker Aug. 31, 1948 2,459,616 Burgwin Jan. 18, 19492,461,283 Jordan Feb. 8, 1949 2,470,443 Mittelmann May 17, 19492,473,188 Albin June 14, 1949 2,487,432 Fuge Nov. 8, 1949 2,504,754Sweeny Apr. 18, 1950 FOREIGN PATENTS Number Country Date 439,166 GreatBritain Dec. 2, 1935

